Re: [RFC/PATCH] Make powerpc64 use __thread for per-cpu variables

Paul Mackerras
2006-05-10T21:05:34Z

David S. Miller writes:

> From: Richard Henderson <rth@twiddle.net>
> Date: Wed, 10 May 2006 08:47:13 -0700
>
> > How do you plan to address the compiler optimizing
> ...
> > Across the schedule, we may have changed cpus, making the cached
> > address invalid.
>
> Per-cpu variables need to be accessed only with preemption
> disabled. And the preemption enable/disable operations
> provide a compiler memory barrier.

No, Richard has a point, it's not the value that is the concern, it's
the address, which gcc could assume is still valid after a barrier.
Drat.

Paul.